Fainting occurs when you don't get enough blood flow to your brain, usually due to a drop in blood pressure. While a low-calorie diet won't necessarily cause fainting, certain conditions that could occur when following this type of diet could lead to fainting if you aren't careful. Eating a well-balanced diet, drinking plenty of fluids and not limiting calories excessively will help minimize this risk.

Low Blood Sugar

Don't skip meals when trying to lose weight. Not only could this backfire and cause you to overeat at your next meal, it could also lead to fainting. If you wait too long between meals and snacks, your blood sugar could drop too low, causing you to faint. Although this is more common in diabetics, it can happen to those who aren't diabetic as well.

Not Getting Enough Nutrients

If your low-calorie diet is too restrictive, you may not get enough of the nutrients needed to form healthy blood cells, such as iron and vitamin B-12. This could cause anemia and minimize the amount of oxygen that reaches your brain, making you more likely to faint. Iron deficiency is one of the more common micronutrient deficiencies, so to limit this risk, pay particular attention to your iron intake when you're dieting.

Lack of Fluids

Make sure you drink plenty of water or other beverages while following a low-calorie diet, especially if vigorous exercise is part of your weight-loss strategy. If you don't get enough to drink, you could become dehydrated. This could lead to a sudden drop in your blood pressure, causing you to faint. You're more likely to become dehydrated when you exercise in very hot weather because of increased sweating. Keep low-calorie sports drinks on hand to replace lost fluid and electrolytes and minimize the risk of fainting.

Other Considerations

Fainting could be due to any number of other causes, including serious medical conditions such as heart problems or diabetes, so tell your doctor if you faint, especially if it occurs more than once. Being stressed, hyperventilating, pregnancy and being in a hot or crowded setting can also bring on a fainting episode. If you start to feel faint, try to lie down or sit with your head between your knees to improve blood flow to your brain.